I own one, and it is a great, versatile amp. It doesn't overdrive as well as a 300T or an SVT 2, and is a bit more of a clean sound, but still with some tube grit. There are A LOT of threads on the 400+. Use the search function here for more details.

I have a 400+. I have a Sunn 300T (Fender Bassman 300) I used to have an SVT 2 Pro. I have used them with the same cabs and the same basses.

All great sounding, loud tube amps. The 400+ and the Ampeg weigh about the same, both being rackmount units. The 300 weighs 8 1/2 metric tons. The 400+ and the 300 will work at 2 4 or 8 ohms, the Ampeg only 2 or 4. The 400+ has the most speaker hookup options - lots of jacks.

Tonally very different. The 400+ does not distort well, but stays clean very loud. It has a very colored sound, IMO even the graphic EQ does not change its fundamental character, just shapes it, but does this well. It's hard to describe in words... strong low mids, great rock tone. The ultra lows aren't too strong, It's not my favorite amp for my string (though I tune down to A).

The Ampeg sounds, well, like an Ampeg. It too has a switchable graphic, but it really does best a big mid heavy old school tone. Very nice distortion, musical and smooth. It was hard to part with it.

The Fender/Sunn is the cleanest of the lot. Super loud. For a tube amp, it sounds pretty uncolored before you start messing with the EQ. The best lows of the 3. The distortion is more guitarish than the Ampeg, on the harsh side and sounds best when blended with the clean sound. I like that you can blend clean and distorted. Also has a built in 2 band compressor so you can compress the lows but not the highs.

I have a 400+. I have a Sunn 300T (Fender Bassman 300) I used to have an SVT 2 Pro. I have used them with the same cabs and the same basses.

All great sounding, loud tube amps. The 400+ and the Ampeg weigh about the same, both being rackmount units. The 300 weighs 8 1/2 metric tons. The 400+ and the 300 will work at 2 4 or 8 ohms, the Ampeg only 2 or 4. The 400+ has the most speaker hookup options - lots of jacks.

Tonally very different. The 400+ does not distort well, but stays clean very loud. It has a very colored sound, IMO even the graphic EQ does not change its fundamental character, just shapes it, but does this well. It's hard to describe in words... strong low mids, great rock tone. The ultra lows aren't too strong, It's not my favorite amp for my string (though I tune down to A).

The Ampeg sounds, well, like an Ampeg. It too has a switchable graphic, but it really does best a big mid heavy old school tone. Very nice distortion, musical and smooth. It was hard to part with it.

The Fender/Sunn is the cleanest of the lot. Super loud. For a tube amp, it sounds pretty uncolored before you start messing with the EQ. The best lows of the 3. The distortion is more guitarish than the Ampeg, on the harsh side and sounds best when blended with the clean sound. I like that you can blend clean and distorted. Also has a built in 2 band compressor so you can compress the lows but not the highs.

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Erm, the ampeg weighs alot more than the 400+ , my SVT II is about 85-90lbs in a light 4U case i have, the 400+ is what, 45-50lbs or something?